To support a shaft with stability and resist torsional loads and/or tilting motions, prior art bearings, both of the mechanical and magnetic types, have generally been matched in pairs at opposite ends of the supported shaft. Typically, arranging the magnetic bearings in pairs is complicated by the inherent instability of the bearings about axes other than the axis of the shaft being supported. Two techniques have generally been employed in the past to overcome this instability, viz: (1) to increase the axial separation between the magnetic bearings and (2) to provide active control channels for the angular position of the bearing members to assure that the bearing members lie in a plane at right angles to the shaft axis. In many cases, it is impractical to separate the bearing members to an extent sufficient to attain the required stability. Imposing active controls, rather than passive restraints, on the angular position of the bearing members in a plane at right angles to the shaft being supported tends to defeat the potentially high reliability of a magnetic bearing system.
Radial bearings, of a type disclosed in my U.S. Pat. No. 3,694,041 remove the requirements for the bearing members to be in matched pairs at opposite ends of a shaft. However, experiments since conducted indicate that additional work had to be performed to enable such radial bearings to have the required passive stability in a plane (the x-y plane) at right angles to the shaft axis (the z-axis when the bearing system is properly aligned). In particular, a central shaft carrying disc member, when tilted in the x-y plane in response to an external load, has a tendency to become stable at an angle different from that of an annular member surrounding the disc, i.e., the disc has a tendency to become stable at an angle removed from the x-y plane or to be tilted from its desired position. It has now been found that the tilting tendency occurs because the pole faces of the annulus and disc are displaced from each other along the z-axis and because the disc pole faces extend parallel to the shaft axis. Thereby, as the annular member tilts about the z-axis, corresponding points on the axially displaced pole faces of the disc become separated by different distances from the points on the annulus with which they are normally aligned. For example, a clockwise turning about a vertically oriented z axis causes a point on the pole face below and to the left of the center (the point about which the tilting is presumed to occur) of the disc to initially rotate to and through a radial line extending from the center of the disc through the points on disc pole face and on the pole face of the annulus which is normally aligned with the disc pole face point. This is analogous to a toggle action. Hence, the separation between the normally aligned points below and to the left of the disc center is initially decreased. In contrast, the corresponding aligned points on the pole faces of the disc and annulus above and to the left of the disc center initially and continually turn away from a radial line extending through the point on the annulus with which it is normally aligned. Because of the differential displacement, and the non-linear force displacement character of magnetic force, there are differential forces between the pole faces which are displaced along the z-axis. These differential forces have a tendency to cause further tilting and are not overcome until the annular member reaches a substantial tilt angle away from the z-axis.